Control method with a characteristic curve defined by interpolation points

ABSTRACT

The invention is based on a control method having a characteristic curve ( 1 ) defined by interpolation points ( 3, 4, 5, 6, 7 ), the characteristic curve being stored in an electronic processing unit. To control stability and with sufficient accuracy processes overridden by strong, time-variant disturbances, it is proposed that a characteristic line ( 1 ) is preset and adapted according to a system deviation and a ratio of the difference between a measured point ( 9 ) and an adjacent interpolation point ( 4, 5 ) and the difference between the two interpolation points ( 4, 5 ) adjacent to the measured point ( 9 ).

BACKGROUND OF THE INVENTION

The invention relates to a control method with a characteristic linedefined by interpolation points.

Processes overridden by strong, time-variant disturbances, in general,can be only insufficiently conducted by adding a linear regulator. Toobtain the required excellence, there have to be used, as a rule,non-linear control loop structures and includes a pattern fordisturbances. This often results in unstable situations. In practice,the disturbance pattern is mostly unknown and a finding is possible onlyat considerably expense, but often is also absolutely impossible.

In such cases, reference is had to a controlled standard of correctingvariables on the basis of a stationary, empirical process pattern with acharacteristic curve or a characteristic field without first taking intoaccount the disturbances. The resulting guiding behavior is stationarilyaccurate for an undisturbed operation case and in the dynamictransition, very quick and yet stable. In case, disturbances occurstationarily unforeseeable deviations of s a greater or smallermagnitude, generate between the regulating variable and the commandvariable. Therefore, it has to be ensured, e.g. by limiting thecorrecting variables, that no critical operating states occur. Ofcourse, it is no longer possible, in this case, sufficiently to meet thegeneral requirements relative to stationary precision.

The invention is based on the problem of stably and with sufficientaccuracy controlling a process that are overridden by strong,time-variant disturbances.

SUMMARY OF THE INVENTION

According to the invention, a control method is selected having acharacteristic curve defined by interpolation points. The interpolationpoints can be empirical values obtained by testing, however they canalso be arbitrarily preset, since they are adapted during the operationspecifically in accordance with the system deviation of a correctingvariable and a ratio of the difference between a measured point and aninterpolation point and the difference between the two interpolationpoints adjacent to the measured point.

Correction values needed for the adjacent interpolation points areconveniently figured out from the following equations:

K _(u) =R _(abw)*[1−(x−x _(u))/(x _(o) −x _(u))

and

K _(o) =R _(abw)*[1−(x _(o) −x)/(x _(o) −x _(u))

wherein K_(o), K_(u) are correction values respectively for the lowerand the upper interpolation points, x is an actual measured operatingpoint on the characteristic curve and x_(o), x_(u) values of a closestupper or lower interpolation point based on the measured value. The newadapted characteristic curve results from the initial interpolationpoints plus the appertaining correction values.

To increase the stability of the method and lightly to load theprocessing unit, it is convenient to perform the adaptation with ascanning time of more than 20 milliseconds. The scanning time must, ifneed be, adapted to the prevailing method time constant. It is furtheradvantageous to limit the adaptation range of the characteristic curvein which an appertaining sensor works linearly. This is simpler in acontrol than in a regulation.

According to another embodiment of the invention, the new interpolationpoints are preset in steps. Excessively great bounces are therebyprevented during the operation and the output variable of the controlproceeds less hectically.

From the correction values conclusions can be drawn on the operatingbehavior. Thus, correction values can be used for diagnosis purposeswhen, e.g. they exceed the preset limit values. On the other hand,defined theoretical values can be preset in order to test the reactionof the systems.

The inventive control method is especially adequate for pressure controlof an automatic transmission, in particular, one with continuouslyvariable ratio. The hydraulic adjustment of the static friction forcebetween two friction elements such as an alternate belt and bevelpulleys is overridden by numerous time-variant disturbances. It must bedynamically and stationarily ensured concerning the contact pressure ofthe bevel pulleys that the belt, such as a sliding link belt, in no caseskids over the bevel pulleys. The bevel pulleys and mainly the beltwould thereby be destroyed. In addition, the contact pressure forceproduced by a hydraulic pressure decisively influences the efficiency ofthe transmission and thus directly the fuel consumption of the drivenmotor vehicle. Therefore, in the control of the contact pressure areinforced crucial point is that there be kept the stationary accuracy.The inventive control method satisfies the requirements in relation bothto the stability of the control and to the accuracy.

When the correction value gives reason to conclude that an error existsin the system, e.g. when it exceeds a preset limit value, it isconvenient to activate a substitute function of the transmission, suchas an emergency program. When the current supply is switched off, e.g.when the ignition of an internal combustion engine is switched off orthe current supply fails, it is further advantageous to store the datain a memory module (e.g. EEPROM, FLASH) in order that they are againavailable when restarting. During the new start, if the last adaptedcharacteristic curve is used, a long-time adaptation of thecharacteristic curve is obtained during the service life.

The inventive control method can be used not only with characteristiccurve but in the same manner with n-dimensional characteristic fields.The correction values of the interpolation points are separately figuredout for each dimension.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages result from the following description of the drawing.In the drawing are shown, byway of example, diagrams with characteristiccurves for explanation of the invention. The specification and theclaims contain numerous features in combination. The expert willconveniently regard the features separately and make with them logicaladded combination.

In the drawings:

FIG. 1 is a diagram in which the appertaining current intensity of amagnetic valve is applied via a theoretical pressure; and

FIG. 2 is the same diagram with an adapted characteristic curve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the diagram of FIG. 1 is plotted a characteristic curve 1 defined byinterpolation points 3-7. It represents the relationship of atheoretical pressure measured in bar to a current intensity of amagnetic valve measured in mA such as utilizable in automatictransmissions with continuously variable ratio of motor vehicles. Theinterpolation points 3-7 can correspond to empirical values (measuredvalues) or be arbitrarily assumed to begin with. They are stored in anelectronic processing unit. A selected adaption range 2 comprises thepressure values 2 bar to 40 bar which is identical with the workingrange of a pressure sensor.

From a measured pressure value Pist the system deviationp_(abw)=(p_(soil)−p_(ist)) is figured out. Correction values 8 arefigured out from the position of the measured point 9 on thecharacteristic curve 1 relative to the adjacent interpolation points 4and 5 and the adjacent interpolation points 4 and 5 are adaptedaccording to the calculated correction values 8.

From the adapted interpolation points results an adapted characteristiccurve 10 (FIG. 2) with adapted interpolation points 11, 12, 13, 14 onwhich is based the further control and which form the pont of referencefor the next adaptation.

The last adapted characteristic curve is stored at the end of theoperation of the motor vehicle and is used as output characteristic linewhen starting again.

Reference numerals 1 characteristic curve 8 correction value 2adaptation range 9 measuring point 3 interpolation point 10 adaptedcharacteristic curve 4 interpolation point 11 adapted interpolationpoint 5 interpolation point 12 adapted interpolation point 6interpolation point 13 adapted interpolation point 7 interpolation point14 adapted interpolation point

What is claimed is:
 1. A method used in an electronic processing unithaving an adaptable characteristic curve (1) defined by interpolationpoints (3, 4, 5, 6, 7), stored in the electronic processing unit, themethod comprising the steps of the characteristic curve (1) being presetand being adapted according to a system deviation and a ratio of thedifference between a measured point (9) and the adjacent interpolationpoints (4, 5) and the difference between the two interpolation points(4, 5) adjacent to the measured point (9).
 2. The control methodaccording to claim 1, comprising adapting the interpolation points (4,5) adjacent to a measured point (9) with a correction value (8) from thefollowing equations: K _(N) =R _(abw)*[1−(x−x _(u))/(x _(o) −x _(u))]and K _(o) =R _(abw)*[1−(x _(o) −x)/(x _(o) −x _(u))] wherein K_(u) andK_(o) are respective correction values (8) for a lower interpolationpoint (5) and an upper interpolation point (5), x is an actual measuredpoint (9) on the characteristic curve (1) and x_(o) and x_(u) are valuesof a closest higher and lower interpolation point (4, 5), respectively,based on a measured point (9), and R_(abw) is an adaption step.
 3. Thecontrol method according to claim 2, further comprising the step ofusing: R _(abw) =x _(d) ·k to performing the adaption step, where x_(d)is the deviation between the actual value x and a target value and k isa calibration parameter.
 4. The control method according to claim 1,further comprising the step of the control method scanning at aiscanning rate above 20 milliseconds.
 5. The control method according toclaim 1, further comprising the step of limiting a range (2) ofadaptation of the characteristic curve (1), with the characteristiccurve (1) corresponding to a working range of an appertaining measuringsensor.
 6. The control method according to claim 1, further comprisingthe step of presetting new Interpolation point values (11, 12, 13, 14)for the control method in steps.
 7. The control method according toclaim 1, further comprising the step of using a correction value of (8)for diagnosis purposes and, when the correction value of (8) exceeds apreset limit value, concluding that an error in the control methodexists.
 8. The control method according to claim 7, further comprisingthe step of presetting defined theoretical values in order to test asystem reaction.
 9. The control method according to claim 1, furthercomprising the step of using the control method for pressure control ofan automatic transmission which has a continuously variable ratio. 10.The control method according to claim 9, further comprising the step ofactivating a substitute function when the correction value (8) exceeds apreset limit value.
 11. The control method according claim 1, furthercomprising the step of, following completion of the control method,storing a last adapted characteristic curve (10) for use as initialvalue when again starting r.
 12. The control method according to claim11, further comprising the step of storing the data in a memory modulewhile a supply of current is switched off.
 13. The control methodaccording to claim 1, further comprising the step of calculating an-dimensional characteristic field and a correction value (8) for eachdimension.